Process for the production of aromatic hydrocarbons



Patented June I PROCESS FOR THE PRODUCTION OF AROMATIC HYDROCABBONSDonald L. Fuller and Bernard S. Greensfelder, Oakland, Calif., assignorsto Shell Development Company, San Francisco,

of Delaware No Drawing.

Calif., a corporation Application November 1'1, 1942, Serial No. 465,923

13 Claims. (o1. 260-673.5l a

The presentinvention relates to a process for the production of aromatichydrocarbons from naphthenic hydrocarbon fractions of the nature ofgasoline. By "naphthenic hydrocarbon fractions of the nature ofgasoline" is meant hydrocarbon fractions from various sources boilingpredominantly within the gasoline boiling range and containingappreciable concentrations, such as or more, of naphthenic hydrocarbonsin admixture with paramn hydrocarbons and also frequently containingappreciable concentrations volve contacting the naphthenic fraction inthe vapor phase with a dehydrogenating contact mass. In such cases whereit is desired, the aromatichydrocarbons formed by the treatment areremoved or concentrated by one of the various well-known methods such asfractional distillation, solvent extraction, extractive distillation, orby a combination of treatments such as alkylation, followed byfractionation, extraction, etc.

Since the primary reaction involved in the proposed processes is thedehydrogenation of cerof oleflnic hydrocarbons and/or aromatichydrocarbons. More particularly, the invention relates to a process forthe production of aromatic hydrocarbons from such petroleum fractionswherein maximum yields of aromatic hydrocarbons ma be the mosteconomically produced by a combination of three separate catalytictreatments. The invention also relates to the production of arcmatichydrocarbons from such fractions by two sub-combination treatmentsinvolving the use of two catalysts which may advantageously be employedin certain cases.

Many hydrocarbon fractions of the nature of gasoline derived fromnaphthenic basepetroleums and from certain conversion processes andbydrocarbon syntheses contain appreciable concentrations of naphthenichydrocarbons. These various fractions usually contain appreciable concentrations of paraiiln hydrocarbons and many of them also contain inaddition appreciable concentrations of oleflnic hydrocarbons and/oraromatic hydrocarbons. The paraflin hydrocarbons generally arepredominantly the normal isomers, the monomethyl isomers being next infrequency of occurrence. The naphthenic hydrocarbons in such distlllatesconsist, in general, of complex mixtures of naphthenic hydrocarbonshaxing sixmembered rings and naphthenic hydrocarbons havingilve-membered rings. The naphthenic hydrocarbons having six-memberedrings (that is, cyclohexane and its homologues) may be easily convertedby dehydrogenation to benzene and the 7 corresponding alkyl benzenes. I

In view of the relative ease with which hydroaromatic naphthenichydrocarbons may be dehydrogenated to corresponding aromatichydrocarbons, numerous processes have been developed for the catalytictreatment of such distillates under dehydrogenation conditions toproduce distillates of more aromatic character. In certain instanceswhere the catalytic dehydrogenation treatment is sufliciently eilicient,it "has proved practical to pro- Y duce substantially pure aromatichydrocarbons by such treatment. These various all intain of thenaphthenie hydrocarbons into the corresponding aromatic hydrocarbons, itis not surprising that nearly all of the many known dehydrogenationcatalysts have been found to be effective for this treatment. Thus, ithas been proposed to effect such treatment with various compounds suchas the oxides, halides, sulfides, chromates, tungstates, molybdates,phosphates, borates, phosphites, chromites, manganates, etc., of suchmetals as Cu, Mg, Ca, Zn, Cd, Ba, B, Al, La, Tl, Si, Ti, Zr, Sn, Pb, Pt,Th, V, Nb, Sb, Ta, Bi, Cr, Se, Mo, Te, W, U, Mn, Re, Fe, Co, Ni, Ru, Pd,Rh, Ce, Pr and others. Also, many special catalystscontaining one ormore of these dehydrogenating compounds usually in combination with oneor more other materials have been developed for this purpose and therelative merits of these various catalysts have been studied. Theappraisal of these various proposed catalysts has been based upon suchfactors as the increase in octane number of the distillate, the increasein the aromaticity of the distillate, the reaction conditions requiredto eflect these improvements in octane number and aromaticity, thethermal stability of the catalyst, the case with which the catalyst canbe prepared, the ease with which the catalyst can be regenerated whenspent, the car- =hon-forming tendency under the reaction conditions, thesusceptibility of the catalyst to be poisoned by sulfur compounds,nitrogen bases, etc., found in such distlllates, and similar practicalaspects of their use. It has not been generally appreciated, however,that many oi these catalysts, although they give substantiallyequivalent Liquid hourly space have now found that by the application ofcombinations oi two or three types of dehydrogenation catalysts inseries much greater conversionstoaromatlchydrocarbonsmaybeobtainedthanbytheuseofanyonetypeofdehydrogenation catalyst alone. In fact, bythe process oi the present invention, it i possible to convert mphthenicfractions of the class described and consisting of hydrocarbons havingsix or'seven carbon atoms entirely into benzene or toluene.respectively. Furthermore, the desirable result may be obtained whilerealizing much better catalystlifeandprocessefiiciencythanhasbeenpossible in most of the hitherto-proposed processes The process of thepresent inventionis applicafractions to be treated are the so-called Csand/or C1 and/or 0: fractions from naphthenic straight run, crackedand/or reformed stocks consisting essentially of the hydrocarbons havingsix and/or seven and/or eight carbon atoms, respectively.

The material to be treated is, according to the present process, treatedwith two or three separate dehydrogenation catalysts under suitableconditions. According to the one aspect of the invention, the materialis treated-first under dehydrogenation conditions (with respect tohydroaromatic hydrocarbons) with a dehydrogenating' metal sulfide.

For this treatment any of the known metal sulfide dehydrogenationcatalysts may be employed. Thus, for example, onemay apply catalystsconsisting largely of one or more sulfides of Fe, Co, Ni, M0 or W.Particularly suitable catalysts, for example, comprise substantialproportions of tungsten sulfide, preferably in,

combination with a sulfide of a metal selected from group VIII, forexample Fe, Co or Ni. These catalysts are employed in the presentprocess under dehydrogenation conditions. Dehydrogenation conditionsmost suitable for catalysts of this type are different from theconditions used in destructive hydrogenation and are usually diilerentfrom the conditions most suitable for dehydrogenation with catalysts ofthe oxide type. Suitable dehydrogenation conditions with respect totemperature, pressure, partial pressure of hydrogen and space velocitydepend somewhat upon the particular catalyst but are, in general, withinthe following limits:

Temperature -..C About 425-550 Pressure ..atmospheres About 10-70Partial pressure of hydrogen atmospheres About 8-60 velocity About0.5-4.0

-Naphthenic gasoline fractions when treated under these conditions withthese catalysts are considerably aromatized. Thus, for example, in thecase of the treatment of straight run fractions the products from thistreatment are found to contain between about 20% and 40% aromatichydrocarbons. Unsaturated hydrocarbons such asolefins, if present in thefeed, are substantially completely hydrogenated. The aromatichydrocarbons formed in this step of the asvaaoo V Iprocessmayberemovediromtheproductiidesired,byany-oneoftlmseveralknownmethods.

For example, the aromatic hydrocarbons may be removed from the productby extraction with one ofthemanysolvents, forexampleSOaaniline, etc.,having a selective solvent action for aromatichydrocarbonaoritmayinsomecasesbesimply fractionally distilled to recovera pureor relatively concentrated aromatic fraction, or the aromatichydrocarbon may be conveniently separated by an extractive distillationin a known manner.

The product from the above-described first ste of the process. eitherwith or without subsequent removal of the aromatic hydrocarbons formed,is contacted under dehydrogenation conditions with a molybdenum oxidecatalyst. Any of the molybdenum oxide hydrotorming catalysts may beemployed. Very suitable catalysts, for example, comprise 4% to 30%molybdenum oxide on a suitable adsorptive support such as absorptivealumina, adsorptive magnesia, activated clay, or the like. Molybdenumoxide supported (15%) on adsor'ptive alumina is an especially goodcatalyst for this purpose. Suitable dehydrogenation conditions withrespect to temperature, Pressure, partial pressure of hydrogen and spacevelocity are chosen within the following approximate limits:

Temperature C About 425-550 Pressure atmospheres About 2-50 Partialpressure of hydrogen atmospheres. About 1-40 Liquid hourly spacevelocity About 0.1-4.0

lyst. Any of the chromium oxide dehydrogeuation catalysts may beemployed. Thus, for example, one may use precipitated and pllledcatalysts consisting of CtaOs, CnOe-AlzOa,

ClaOa-AhOs-KrO, CraO's-SlOz, CraOs-Zi'O: C1'2O:M'8O, etc. Also, one mayuse chromium Temperature C'. About425-550 Pressure g atmospheres About0.1-7 Partial pressure of hydrogen I atmospheres-.. 0.5 Liquid hourlyspace The product from the treatment with the chromium oxide catalystmay, if desired, be used per se or may be treated to recover aromatichydrocarbons in -a pure or more concentrated form. The aromatic contentof this product depends upon whether or notaromatic hydrocarbons havebeen removed after the first or second of the above-describeddelwdrogenation treatments. I!

aromatic hydrocarbons have beenremoved from the product after the firstand/or second dehydrogenation treatment, this product usually containsabout 50% aromatic hydrocarbons. If aromatic hydrocarbons have beenremoved only after the first dehydrogenation step, aromatic contents oiabout 70% are usually present. It aromatic the first or second of theabove-described dehydrogenation steps, the aromatic content of thisproduct is much higher, for example 80%. It the aromatic hydrocarbonsformed are removed from hydrocarbons have not been removed after eithera the product after the chromium oxide treatment,

the non-aromatic fraction may, if desired, be recycled back to thechromium oxide treatment. In this way substantially complete conversionof the naphthenic fraction to aromatic hydrocarbons may be obtained.

In the above, the process has been described as comprising threeseparate dehydrogenation treatmerits under three definitedehydrogenation conditions with three separate types of dehydrogenationcatalyst. This three-step process gives optimum results. It is notnecessary, however, that the complete efilciency of the above-describedthree-step process be utilized. The invention also contemplates twosub-combinations oi! this three-step process which, while not asefilcient as the three-step process, are nevertheless superior to any ofthe single-step processes heretofore proposed and may be profitablyemployed, for e ample, where it is desired to avoid the cost ofproviding three separate dehydrogenation units.

The first of these alternative two-step processes involves contactingthe naphthenic hydrocarbon fraction first with a metal sulfidedehydrogenation catalyst as above described in the first step of thethree-step process and then contacting the product, either with orwithout subsequent removal or concentration of aromatic hydrocar- 1bons, with a molybdenum oxide catalyst as described in the second step01 the three-step proccycled to the first dehydrogenation treatment withthe metal sulfide, no appreciable further amounts of aromatichydrocarbons are formed.

By contacting this product, however, under dehydrogenation conditionswith the chromium oxide catalyst as described, additional amounts (forexample, 10%-70%) of aromatic hydrocarbons are formed. 'It is also to benoted that ii the material is contacted with the various dehydrogenationcatalysts in any other way, appreciable increase in yield of aromatichydrocarbons over that obtained by the conventional one-step process isnot obtained. Thus, if the naphthenic i'raction is contacted with themolybdenum oxide or chromium oxide catalyst first, only very smallamounts of aromatic hydrocarbons are Iormed by subsequent contacting 01'this material under dehydrogenation conditions with the metal sulfidecatalyst, or it the material is contacted with the chromium oxidecatalyst prior to contacting it with the molybdenum oxide catalyst, thedehydrogenation with the molybdenum oxide catalyst gives much loweryields of aromatic hydrocarbons than those obtained with thechromium-oxide catalyst in. the last step 0! the described process, andthe catalytic Me of the ess. It will be observed that this alternativeprocessis the same as the above-described threestep process except thatthe dehydrogenation treatment with a chromium oxide catalyst is omitted.

chromium oxide catalyst is round to be very poor.

A suitable application of the process is illustrated by the iolowingexample:

A hydrocarbon traction consisting essentially 01 a mixture of normalparamn and cycloparaifin hydrocarbons of both hydroaromatic andnonhydroaromatic character was treated with a tungsten sulfide-nickelsulfide catalyst under the folowing conditions: Temperature C 4'75Pressure atmospheres 25 M01 ratio of hydrogen to'hydrocarbon 8 Liquidhourly space velocity 1.0

According to the second alternative two-step I process, the naphthenicpetroleum traction, preterably a straight run gasoline fraction, isfirst contacted with a molybdenum oxide catalyst as described in thesecond step of the three-step process and the product, either with orwithout subsequent removal or concentration of aromatic hydrocarbons, istreated with a chromium oxide catalyst as described in the third step ofthe three-step process. It will be observed that this alternativeprocess is the same as the recycled, no appreciable additional yields ofaro- The product contained about 27% by weight of aromatic hydrocarbons,chiefly toluene. The aromatic hydrocarbons were extracted from theproduct and the non-aromatic portion treated with a molybdenumoxide-alumina catalyst (14% Mo) under the following conditions:

Temperature C 490 Pressure atmospheres 10 Mel ratio of. hydrogen tohydrocarbon 3 Liquid hourly space velocity 0.6

The product contained about 26% by weight of aromatic hydrocarbons. Thearomatic hydrocarbons were extracted trom'the product. The remainingnon-aromatic portion was exceptionally suited for treatment with achromium oxidematic hydrocarbons are obtained. when, however, theproduct from the dehydrogenation treatment with the metal sulfidecatalyst is contacted under dehydrogenation conditions with the mo-Lvbdenum oxide catalyst as described, the product contains considerableadditional aromatic hydrocarbons, for example 20%-40%. Again. ii thearomatic hydrocarbons are removed from this product and thearomatic-free product realumina (11% Cr) catalyst under the followingconditions:

Temperature C 4'75 Pressure atmospheres 1 Mol ratio of hydrogen tohydrocarbon 0 Liquid hourly space velocity, 0.4

The ultimate yield 0! aromatic hydrocarbons obtained by the abovecombination of steps is higher than could be obtained with the saidhydrocarbon fraction by the same number of passes with any one of thethree catalysts separately or by any other order 0! the threetreatments.

we claim as our invention:

1. A process for the production of aromatic hydrocarbons from naphthenicfractions of the nature of gasoline which comprises contacting thenaphthenic gasoline fraction under dehydrogenaflmconditicnsflrstwltha'oxidecatalyst ing metal sulfide catalyst.thenwithamolybchosen'withinthetollowinglimih.

denum odds and then Q m o c Pressure .a AboutHn2.111emlordhgtoclflml1lnrdn the metal dehydrogenation catalyst com- 3.W140- Pm mm Liquid hourly space velocity.--" About 0.1-4.0

a r The process according to claim. 6 wherein the me s e one on ccomprises tun sten sulfide and nickel sulfide. 10 the mi'lheproceasaccordingtoclaimlwherein the molybdenum oxide catalystconsists essentialiy oi molybdenum oxide supported upon alumine. I

5.111epr0cessaccordingtoclaim1wherein the chromium oxide catalystconsists essentially of chromium oxide and alumina.

6. A process for the production oi aromatic hydrocarbons from naphthenicfractions of the nature of gasoline which comprises contacting thenaphthenic fraction with a metal sulfide dehydrogenation catalyst underconditions chosen within the following limits:

Temperature 0-- About 425-550 Pressure -atmospheres About 10-70 Partialpressure of hydrogen atmospheres" About s-oo Liquid hourly spacevelocity About 0.5-4.0

P118123 tungsten sulfide.

8.'lheprocessaccordingioclaimflwher-ein the metal sulfidedehydrosenation catalyst com prises tungsten sulfide and nickel sulfide.

'9.The process accordingtoclaim6wherein the molybdenum oxide catalystconsists essentially or molybdenum oxide supported upon alumina.l0.'l'heprocessaccordingtoclaim1wherein the naphthenic traction consistspredominantly of hydrocarbons having seven carbon atoms.

1i."lhe process according to claim 8 wherein the naphthenictractionconsists predominantly of hydrocarbons having seven carbon atoms.

12. The process according to claim 1 wherein aromatic hydrocarbonsproduced are removed from the product after each or said catalytictreatments. v

13. The process according to claim 8 wherein aromatic hydrocarbonsproduced are removed from the product prior to the treatment with themolybdenum oxide catalyst.

csnnrrclrs or conmsclzton.

NA L, FULLER, ET s.

It is hereby certified 0nd column, line 36, for -"case" June 12,.1914.5.

I -thai; error appears flue printed speeiiicatidn;

or the above numbered 'patent requiring correction asidllows:

Page 1, sec-1 read- --ease page 2, second column,

61, for "6.5" read o-5-'-; and that, the said Letters -Patent should beism with this correction therein that the the case in the Patent'ofrice.

same may conform to iiie record off (Seall Leslie Frazer FirstAssistant; Commissioner of Patents.

senaibn conditions first with a Willameting metal sulfide catalyst,thenwith a denumoaidecatalystandtbenwlthachromlmn onidecl-talyat.

2.'1he procea according to claim 1 wherein the metal sulfidedehydrogenation catalyst comprisestlmsstensuliide.

a'l'heprocesaccordingtoclaimiwherein the metal sulfide dehydrogenationcatalyst oomhydrogenation catalyst under conditions chosen within thefollowing limits:

Temperature 0-- About 425-550 Pressure -atmospheres About 10-70 Partialpressure of hydrosen atmospheres" About s-so Liquid hourly spacevelocity About 0.5-4.0

to selectively dehvdrogenate naphthenes and hydrogenate any olefinspresent, and then contacting the thus-treated fraction with a molybdenumasnsos oxidecataiystlmdsr cmditim atmospheres Ami-4o- Liquid hourlyspace velocity.--" Amos-4.0

'L'l'heprocesaucording-toclaimflwhereinthemetalsuifidedehydrogenationcatalystcomprise tungstensulfide.

8.'lheprocessaccordingtoclainrflwher-ein the metal sulfidedehydrasenation catalyst com prises tungsten sulfide and nickel sulfide.

'9.The process accordingtoclaim6wherein the molybdenum oxide catalystconsists essentially or molybdenum oxide supported upon alumina.l0.'1'heprocessaccordingtoclaim1wherein the naphthenic traction consistspredominantly of hydrocarbons havins seven carbon atoms.

IL'The process according to claim 8 wherein the naphthenictractionconsists predominantly of hydrocarbons having seven carbon atoms.

12. The process according to claim 1 wherein aromatic hydrocarbonsproduced are removed from the product after each or said catalytictreatments. v

13. The process according to claim 8 wherein aromatic hydrocarbonsproduced are removed from the product prior to the treatment with themolybdenum oxide catalyst.

DONALD L. FULLER. BERNARD S. GREENBFELDm.

csnnrrcirs or conmscizton.

It is hereby certified 0nd column, line 36, for -"case" DONAL]? L,FULLER, ET at.

June 12,. 1914.5.

I -that error appears the printed speeiiicatidri;

oi the above numbered 'patent requiring correction esfdllows:

Page 1, see-1 read- --ease page 2, second column,

61, roi- "6.5" read o-5-'-; and that, the said Letters Patent should beitem with this correction therein that the the case in thePatent'ofrice.

same mayv conform to the record off Signed a sealed t i 2n d y orOctober, A. p. 1 9s Leslie Frazer

